Communicable Disease Control: Immunisation

This section covers:

• The design, evaluation, and management of immunisation programmes
• Choices in developing an immunisation strategy
  

Immunisation

Aim of immunisation: to provoke immunological memory to protect individual against a particular disease

Two types of immunisation:

• Passive: temporary protection e.g. Immunoglobulin (Ig's)
• Active: longer term protection leading to the formation of antibodies

Types of vaccines

Live vaccine (attenuated)

• Measles Mumps Rubella (MMR), oral polio, Bacille Calmette Guerin (BCG), Yellow Fever
• single dose
• long duration of immunity
• less stable: may revert to a virulent strain
• can cause disease in immuno-suppressed, (exception is HIV patients where do recommend, apart from BCG)

Inactivated vaccine (killed)

• Diphtheria Tetanus Pertussis (DTP), typhoid, Hepatitis B, flu, rabies, meningitis C, Hib
• multiple doses and booster
• short immunity
• stable

Contra indications to immunisation

• very few real contra-indicators
• severe reaction to previous dose
• immuno-suppression (no live vaccines)

Vaccine failure

• primary: individual fails to make adequate immune response to initial vaccination
• secondary: individual makes initial adequate response, but then immunity wanes over time

Vaccination programmes

Development of a Vaccine Programme

• Prior to designing a vaccine programme, must establish
  • Is there a need for the programme? - does the disease cause a significant public health problem
  • Is a suitable vaccine available that is safe and effective?

Aim of Immunisation Programme

• To protect those at highest risk (selective immunisation strategy
  OR
• To eradicate, eliminate or contain disease (mass immunisation strategy)

Vaccination strategies

A. Selective Vaccination

• Given to those at increased risk
• Examples - for travel e.g. Hepatitis A; occupational e.g. Hepatitis B; chronic disease e.g. Splenectomy - meningococcal, Hib; outbreak e.g.Hepatitis A

B. Mass Vaccination

Either

• Eradication - Disease and its causal agent have been removed worldwide e.g. small pox
• Elimination - Disease has disappeared from one WHO region but remains elsewhere e.g. polio
• Containment - The point at which the disease no longer constitutes a 'significant public health problem' e.g. Hib

Issues in Vaccine Policy Decisions

• Aim of programme
• Cost of programme
• Population accessibility
• Cultural attitudes and practices
• Facilities available for delivery

The need for a vaccination programme depends on:

• disease incidence
• age distribution of disease
• disease trends
• disease complications
• mortality
• population / cultural attitudes
• cost and benefit
• political expenditure
• vaccine efficacy and side effects
• availability and validity of delivering
• provision of trained primary care providers
• vaccine type

Development of a vaccination programme

Plus: pharmo-economic studies - Cost Benefit Analysis (CBA) / Cost Effective Analysis (CEA) (at phase 3)

Implementation of a vaccination policy

• choice of policy - mass or selective
• publish recommendations ('green book': Immunisation Against Infectious Disease)
• license vaccine
• purchase vaccine
• Then, media campaign and start giving vaccinations

Factors associated with low immunisation coverage

1. socio-demographic variables
   • deprived, inner city living
   • mobile families
   • birth order, large families
   • children with chronic illnesses
   • ethnicity
2. personal variables
   • parents
   • professionals
3. health service variables - generally good in the UK, but be aware of some limitations
   • poor co-ordination (private and public sectors)
   • unclear responses
   • access to guidelines and policies

UK initiatives leading to improved coverage in 1990s

• 1986: district immunisation co-ordinator appointed
• 1987: rapid monitoring and feedback of coverage data - COVER statistics
• 1988: national guidelines on immunisation
• 1990: accelerated immunity schedule
• 1990: GP contracts - financial incentives
• 1992: parent-held records
• national vaccination campaigns - intermittent (e.g. MMR/Hib)
• other:
  • opportunistic delivery
  • specific immunisation clinics
  • targeted information campaigns

  UK immunisation service is consider a world example

• initiated by birth notification on 'Child Health System'
• Community Health Service (CHS) computer generates automatic letters inviting children for vaccination, and ensures GP call and recall for immunisation

Vaccine Coverage

COVER (Cover of Vaccination Evaluated Rapidly)

• Since 1988 computerised child health records contain vaccination details of all resident children. These are completed each time a vaccine is given by a healthcare professional
• Every 3 months information is collated from these child health systems to identify the number of children who have completed vaccine courses at 1, 2 and 5 years of age and fed to the HPA
• The data is fed back to local healthcare workers, immunisation co-ordinators and the PCT to improve coverage

Uses

• Detect change rapidly and monitor trends in uptake
• Look for pockets of poor coverage
• Estimate vaccine efficacy
• Measure impact and success of a vaccination campaign

Evaluation of Vaccine Programmes

• Disease incidence
• Susceptibility
• Vaccine Coverage
• adverse events and vaccine safety

Monitoring Adverse Events and Vaccine Safety

• Committee on Safety of Medicines (CSM) advises the Medicines and Healthcare products Regulatory Agency (MHRA) on safety, quality and efficacy of vaccines
• MHRA responsible for Yellow Card Adverse Drug Reaction reporting system
• Yellow Card reports can signal possibility that a product may be associated with certain risks. These can then be investigated further to decide whether a side effect is truly from a vaccine or not

United Kingdom childhood vaccination schedule 2006

© Sarah Anderson, Gayatri Manikkavasagan 2008